The present invention relates to a master cylinder which is used for various brake devices.
One example of a conventional master cylinder is shown in FIG. 4. In the master cylinder of this type, a cylinder housing 51 is constructed by screwing a cap 53 into the opening of a body 52. A piston guide 54 is disposed in the cylinder housing 51, and a piston 55 which is guided and supported by the piston guide 54 is slidably installed. A vertical hole 56 is formed in the piston guide 54, and a passage 58 communicating with an oil reservoir 57 is open to a pressure chamber 59 when the master cylinder is not operated.
On the peripheral surface of the piston 55 is formed a through hole 60. When the through hole 60 coincides with the vertical hole 56 of the piston guide 54, the oil reservoir 57 communicates with the pressure chamber 59. Therefore, if the oil in the pressure chamber 59 becomes insufficient, oil is supplied from the oil reservoir 57 to the pressure chamber 59. An annular seal member 61 is installed on the end surface of the piston guide 54 on the pressure chamber 59 side.
With the master cylinder of this type, the piston 55 is pushed into the pressure chamber 59 by a push rod, not shown. When the through hole 60 of the piston 55 passes through the annular seal member 61, the through hole 60 is closed, thereby the communication between the through hole 60 and the vertical hole 56 of the piston guide 54 is cut off. Therefore, when the piston 55 is further pushed into the pressure chamber 59, the oil in the pressure chamber 59 is sent under pressure to a brake system of a not illustrated wheel cylinder, etc. On the peripheral surface of the body 52 is installed a mount 62 for a not illustrated brake booster.
In the conventional master cylinder described above, however, the cap 53 and the piston guide 54 are constructed separately, so that a clearance is formed at position D where the outer peripheral surface of the piston guide 54 fits on the inner peripheral surface of the cap 53, as well as at position A where the brake booster (not shown) is installed to the mount 62 of the body 52, position B where the cap 53 is screwed in the body 52, and position C where the outer peripheral surface of the piston 55 slides on the inner peripheral surface of the piston guide 54. Therefore, when the master cylinder is mounted on the brake booster, which is a mating member, not shown, the concentricity with the brake booster cannot be achieved sufficiently due to the clearances at the four positions, thereby the output efficiency is lowered. With the conventional master cylinder, the number of parts increases because of the presence of the piston guide 54; accordingly, the number of working processes increases and the assembly work becomes complicated. Therefore, the conventional master cylinder has the disadvantages that it is not suitable for mass production and the part cost is high.